/*
 * Copyright 2001-2004 Unicode, Inc.
 * 
 * Disclaimer
 * 
 * This source code is provided as is by Unicode, Inc. No claims are
 * made as to fitness for any particular purpose. No warranties of any
 * kind are expressed or implied. The recipient agrees to determine
 * applicability of information provided. If this file has been
 * purchased on magnetic or optical media from Unicode, Inc., the
 * sole remedy for any claim will be exchange of defective media
 * within 90 days of receipt.
 * 
 * Limitations on Rights to Redistribute This Code
 * 
 * Unicode, Inc. hereby grants the right to freely use the information
 * supplied in this file in the creation of products supporting the
 * Unicode Standard, and to make copies of this file in any form
 * for internal or external distribution as long as this notice
 * remains attached.
 */

/* ---------------------------------------------------------------------

    Conversions between UTF32, UTF-16, and UTF-8. Source code file.
    Author: Mark E. Davis, 1994.
    Rev History: Rick McGowan, fixes & updates May 2001.
    Sept 2001: fixed const & error conditions per
	mods suggested by S. Parent & A. Lillich.
    June 2002: Tim Dodd added detection and handling of incomplete
	source sequences, enhanced error detection, added casts
	to eliminate compiler warnings.
    July 2003: slight mods to back out aggressive FFFE detection.
    Jan 2004: updated switches in from-UTF8 conversions.
    Oct 2004: updated to use UNI_MAX_LEGAL_UTF32 in UTF-32 conversions.

    See the header file "ConvertUTF.h" for complete documentation.

------------------------------------------------------------------------ */



#ifdef CVTUTF_DEBUG
#include <stdio.h>
#endif

#include "fs_tools.h"
#include "fs_unicode.h"

static const int halfShift = 10;	/* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
// Used for UTF82UTF16 static const UTF32 halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START  (UTF32)0xD800
#define UNI_SUR_HIGH_END    (UTF32)0xDBFF
#define UNI_SUR_LOW_START   (UTF32)0xDC00
#define UNI_SUR_LOW_END     (UTF32)0xDFFF
#define false	   0
#define true	    1

/* --------------------------------------------------------------------- */


/* --------------------------------------------------------------------- */

/*
 * Index into the table below with the first byte of a UTF-8 sequence to
 * get the number of trailing bytes that are supposed to follow it.
 * Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
 * left as-is for anyone who may want to do such conversion, which was
 * allowed in earlier algorithms.
 */
static const char trailingBytesForUTF8[256] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1,
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
    4, 4, 4, 4, 5, 5, 5, 5
};

/*
 * Magic values subtracted from a buffer value during UTF8 conversion.
 * This table contains as many values as there might be trailing bytes
 * in a UTF-8 sequence.
 */
/* Used for UTF82UTF16 
static const UTF32 offsetsFromUTF8[6] =
    { 0x00000000UL, 0x00003080UL, 0x000E2080UL,
    0x03C82080UL, 0xFA082080UL, 0x82082080UL
};
*/

/*
 * Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
 * into the first byte, depending on how many bytes follow.  There are
 * as many entries in this table as there are UTF-8 sequence types.
 * (I.e., one byte sequence, two byte... etc.). Remember that sequencs
 * for *legal* UTF-8 will be 4 or fewer bytes total.
 */
static const UTF8 firstByteMark[7] =
    { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

/* --------------------------------------------------------------------- */

/* The interface converts a whole buffer to avoid function-call overhead.
 * Constants have been gathered. Loops & conditionals have been removed as
 * much as possible for efficiency, in favor of drop-through switches.
 * (See "Note A" at the bottom of the file for equivalent code.)
 * If your compiler supports it, the "isLegalUTF8" call can be turned
 * into an inline function.
 */

/* --------------------------------------------------------------------- */

ConversionResult
fs_UTF16toUTF8(FS_INFO * fs, const UTF16 ** sourceStart,
    const UTF16 * sourceEnd, UTF8 ** targetStart,
    UTF8 * targetEnd, ConversionFlags flags)
{
    ConversionResult result = conversionOK;
    const UTF16 *source = *sourceStart;
    UTF8 *target = *targetStart;
    while (source < sourceEnd) {
	UTF32 ch;
	unsigned short bytesToWrite = 0;
	const UTF32 byteMask = 0xBF;
	const UTF32 byteMark = 0x80;
	const UTF16 *oldSource = source;	/* In case we have to back up because of target overflow. */
	ch = getu16(fs, (uint8_t *) source);
	source++;

	/* If we have a surrogate pair, convert to UTF32 first. */
	if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
	    /* If the 16 bits following the high surrogate are in the source buffer... */
	    if (source < sourceEnd) {
		UTF32 ch2 = getu16(fs, (uint8_t *) source);
		/* If it's a low surrogate, convert to UTF32. */
		if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
		    ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
			+ (ch2 - UNI_SUR_LOW_START) + halfBase;
		    ++source;
		}
		else if (flags == strictConversion) {	/* it's an unpaired high surrogate */
		    --source;	/* return to the illegal value itself */
		    result = sourceIllegal;
		    break;
		}
	    }
	    else {		/* We don't have the 16 bits following the high surrogate. */
		--source;	/* return to the high surrogate */
		result = sourceExhausted;
		break;
	    }
	}
	else if (flags == strictConversion) {
	    /* UTF-16 surrogate values are illegal in UTF-32 */
	    if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
		--source;	/* return to the illegal value itself */
		result = sourceIllegal;
		break;
	    }
	}
	/* Figure out how many bytes the result will require */
	if (ch < (UTF32) 0x80) {
	    bytesToWrite = 1;
	}
	else if (ch < (UTF32) 0x800) {
	    bytesToWrite = 2;
	}
	else if (ch < (UTF32) 0x10000) {
	    bytesToWrite = 3;
	}
	else if (ch < (UTF32) 0x110000) {
	    bytesToWrite = 4;
	}
	else {
	    bytesToWrite = 3;
	    ch = UNI_REPLACEMENT_CHAR;
	}

	target += bytesToWrite;
	if (target > targetEnd) {
	    source = oldSource;	/* Back up source pointer! */
	    target -= bytesToWrite;
	    result = targetExhausted;
	    break;
	}
	switch (bytesToWrite) {	/* note: everything falls through. */
	case 4:
	    *--target = (UTF8) ((ch | byteMark) & byteMask);
	    ch >>= 6;
	case 3:
	    *--target = (UTF8) ((ch | byteMark) & byteMask);
	    ch >>= 6;
	case 2:
	    *--target = (UTF8) ((ch | byteMark) & byteMask);
	    ch >>= 6;
	case 1:
	    *--target = (UTF8) (ch | firstByteMark[bytesToWrite]);
	}
	target += bytesToWrite;
    }
    *sourceStart = source;
    *targetStart = target;
    return result;
}

/* --------------------------------------------------------------------- */

/*
 * Utility routine to tell whether a sequence of bytes is legal UTF-8.
 * This must be called with the length pre-determined by the first byte.
 * If not calling this from ConvertUTF8to*, then the length can be set by:
 *  length = trailingBytesForUTF8[*source]+1;
 * and the sequence is illegal right away if there aren't that many bytes
 * available.
 * If presented with a length > 4, this returns false.  The Unicode
 * definition of UTF-8 goes up to 4-byte sequences.
 */

static Boolean
isLegalUTF8(const UTF8 * source, int length)
{
    UTF8 a;
    const UTF8 *srcptr = source + length;
    switch (length) {
    default:
	return false;
	/* Everything else falls through when "true"... */
    case 4:
	if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
	    return false;
    case 3:
	if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
	    return false;
    case 2:
	if ((a = (*--srcptr)) > 0xBF)
	    return false;

	switch (*source) {
	    /* no fall-through in this inner switch */
	case 0xE0:
	    if (a < 0xA0)
		return false;
	    break;
	case 0xED:
	    if (a > 0x9F)
		return false;
	    break;
	case 0xF0:
	    if (a < 0x90)
		return false;
	    break;
	case 0xF4:
	    if (a > 0x8F)
		return false;
	    break;
	default:
	    if (a < 0x80)
		return false;
	}

    case 1:
	if (*source >= 0x80 && *source < 0xC2)
	    return false;
    }
    if (*source > 0xF4)
	return false;
    return true;
}

/* --------------------------------------------------------------------- */

/*
 * Exported function to return whether a UTF-8 sequence is legal or not.
 * This is not used here; it's just exported.
 */
Boolean
isLegalUTF8Sequence(const UTF8 * source, const UTF8 * sourceEnd)
{
    int length = trailingBytesForUTF8[*source] + 1;
    if (source + length > sourceEnd) {
	return false;
    }
    return isLegalUTF8(source, length);
}

/* --------------------------------------------------------------------- */

#if 0
// THIS HAS NOT BEEN COVERTED FOR ENDIAN-ness yet
ConversionResult
fs_UTF8toUTF16(FS_INFO * fs, const UTF8 ** sourceStart,
    const UTF8 * sourceEnd, UTF16 ** targetStart,
    UTF16 * targetEnd, ConversionFlags flags)
{
    ConversionResult result = conversionOK;
    const UTF8 *source = *sourceStart;
    UTF16 *target = *targetStart;
    while (source < sourceEnd) {
	UTF32 ch = 0;
	unsigned short extraBytesToRead = trailingBytesForUTF8[*source];
	if (source + extraBytesToRead >= sourceEnd) {
	    result = sourceExhausted;
	    break;
	}
	/* Do this check whether lenient or strict */
	if (!isLegalUTF8(source, extraBytesToRead + 1)) {
	    result = sourceIllegal;
	    break;
	}
	/*
	 * The cases all fall through. See "Note A" below.
	 */
	switch (extraBytesToRead) {
	case 5:
	    ch += *source++;
	    ch <<= 6;		/* remember, illegal UTF-8 */
	case 4:
	    ch += *source++;
	    ch <<= 6;		/* remember, illegal UTF-8 */
	case 3:
	    ch += *source++;
	    ch <<= 6;
	case 2:
	    ch += *source++;
	    ch <<= 6;
	case 1:
	    ch += *source++;
	    ch <<= 6;
	case 0:
	    ch += *source++;
	}
	ch -= offsetsFromUTF8[extraBytesToRead];

	if (target >= targetEnd) {
	    source -= (extraBytesToRead + 1);	/* Back up source pointer! */
	    result = targetExhausted;
	    break;
	}
	if (ch <= UNI_MAX_BMP) {	/* Target is a character <= 0xFFFF */
	    /* UTF-16 surrogate values are illegal in UTF-32 */
	    if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END) {
		if (flags == strictConversion) {
		    source -= (extraBytesToRead + 1);	/* return to the illegal value itself */
		    result = sourceIllegal;
		    break;
		}
		else {
		    *target++ = UNI_REPLACEMENT_CHAR;
		}
	    }
	    else {
		*target++ = (UTF16) ch;	/* normal case */
	    }
	}
	else if (ch > UNI_MAX_UTF16) {
	    if (flags == strictConversion) {
		result = sourceIllegal;
		source -= (extraBytesToRead + 1);	/* return to the start */
		break;		/* Bail out; shouldn't continue */
	    }
	    else {
		*target++ = UNI_REPLACEMENT_CHAR;
	    }
	}
	else {
	    /* target is a character in range 0xFFFF - 0x10FFFF. */
	    if (target + 1 >= targetEnd) {
		source -= (extraBytesToRead + 1);	/* Back up source pointer! */
		result = targetExhausted;
		break;
	    }
	    ch -= halfBase;
	    *target++ = (UTF16) ((ch >> halfShift) + UNI_SUR_HIGH_START);
	    *target++ = (UTF16) ((ch & halfMask) + UNI_SUR_LOW_START);
	}
    }
    *sourceStart = source;
    *targetStart = target;
    return result;
}
#endif
